Use AgGrid flex to fill container proportionally without squishing columns

fit_columns_on_grid_load shrinks all columns equally. flex distributes
remaining space proportionally to each column's weight so wider columns
stay wider, narrower columns stay narrower, and no scroll occurs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

visualization/betting_page.py

@@ -378,13 +378,23 @@ def _render_sortable_grid(display_df: pd.DataFrame, numeric_df: pd.DataFrame, cs
         )
         gb.configure_column(style_field, hide=True)
     gb.configure_grid_options(headerHeight=38, rowHeight=36, suppressMovableColumns=True, suppressCellFocus=True, ensureDomOrder=True, animateRows=False)
+    grid_options = gb.build()
+    for col_def in grid_options.get("columnDefs", []):
+        field = col_def.get("field", "")
+        if field.startswith("__"):
+            continue
+        col_w = _COL_WIDTHS.get(field, _BOOK_COL_WIDTH)
+        col_def["flex"] = col_w
+        col_def["minWidth"] = max(50, col_w // 2)
+        col_def.pop("width", None)
+        col_def.pop("maxWidth", None)
     response = AgGrid(
         grid_df,
-        gridOptions=gb.build(),
+        gridOptions=grid_options,
         allow_unsafe_jscode=True,
         custom_css=_GRID_THEME,
         theme="balham",
-        fit_columns_on_grid_load=True,
+        fit_columns_on_grid_load=False,
         data_return_mode=DataReturnMode.FILTERED_AND_SORTED,
         update_mode=GridUpdateMode.MODEL_CHANGED,
         height=min(540, max(240, 86 + len(grid_df) * 36)),